Metal oxide nanotube and process for production thereof

ABSTRACT

Spiral shaped fibers were utilized to prepare completely novel metal oxide nanotubes comprising solely metal oxides. The metal oxide nanotubes comprise solely a hollow cylinder shaped metal oxide which may contain hydroxyl groups constituting a double helix and having hole diameter distributions containing two peak hole diameters ranging from 1 to 2 nm and from 3 to 7 nm. The tubes may be obtained by forming spiral shaped fibers from a solution of compound 1  
                 
 
and compound 2  
                 
and using the fibers as a template for making the nanotubes. The hydrogen adsorption and storage capacity of the metal oxide nanotubes are extremely good.

TECHNICAL FIELD

The present invention relates to metal oxide nanotubes consisting solelyof a metal oxide manufactured by using a hydrogel comprising a selfaggregating organic compound as a template, more specifically, to metaloxide nanotubes having hollow cylinder micro structures constituting ametal oxide and having a capability to adsorb and store gas,particularly, a capability to adsorb and store hydrogen.

PRIOR ART

The inventors have been conducting research on the formation ofnanometer sized aggregates through self aggregation in solution oforganic materials having specific structures. (John, G,; Masuda, M;Okada, Y.; Yase, K.; Shimizu, T. Adv. Mater. 2001, 13, 715: Masuda, M.;Hanada, T.; Okada, Y.; Yase, K.; Shimizu, T. Macromolecules 2000, 33,9233.: Nakazawa, I.; Masuda, M.; Okada, Y.; Hanada, T.; Yase, K.; Asai,M.; Shimizu, T. Langmuir 1999, 15, 4757.: Shimizu, T.; Masuda, M. J. Am.Chem. Soc. 1997, 119, 2812.: Japanese Patent Application 2001-239014:Japanese Patent Application 2001-248636.) During such research,nanotubes having excellent abilities to adsorb and store gases,particularly, the capacity to adsorb and store hydrogen, werediscovered.

Carbon nanotubes, carbon fibers and the like having nanometer sizedspaces and voids have been known as materials having such ability toadsorb and store hydrogen. (WO 00/40509. Japanese Patent ProvisionalPublication 2002-54559.) In particular, some of the carbon nanotubesdisplayed hydrogen adsorption and storage capacities of 4% by weight to8% by weight in some experimental examples, but their problems includedhigh pressure conditions that made them impractical to use, measurementsmade at liquid nitrogen temperatures and the inability to perform thefunction repeatedly since they were used only under irreversibleconditions. [For example, J. Richter, R. Seidel, R. Kirsch, M. Merting,W. Pompe, J. Plaschke, H. Schacker, Adv. Mater., 12, 507 (2000). P.Chen, X. Wu, J. Lin, K. L. Tan, Science, 285, 91 (1999).]

In general, a hydrogen adsorption and storage capacity of about 3% byweight is considered necessary for an ordinary passenger vehicle tostore the hydrogen gas needed to travel 500 km, and this is an acceptedpractical target level. However, reported hydrogen adsorption andstorage capacities included about 3% by weight or less for single layercarbon nanotubes, about 1.5% by weight or less for carbon fibers andabout 0.6% by weight for activated carbon although some inconsistenciesexisted, and the goal has hardly been achieved. Furthermore, singlelayer and multiple layer carbon nanotubes have many problems that needto be solved. For example, they are very expensive and are not adaptableto large volume production.

Hydrogen adsorbing and storing alloys, mesoporous materials, porousorganic materials and the like having nanometer sized voids are alsoknown as hydrogen adsorbing and storing materials (Japanese PatentProvisional Publication 2002-105609), but their performance as far ashydrogen adsorption and storage capacity is concerned has not reachedthe level adequate for practical applications. This is particularly trueof hydrogen adsorbing and storing alloys which have high specificgravity, toxicity, contain a rare and expensive metal as an activeingredient or disintegrate into fine powder upon adsorption anddesorption of hydrogen leaving many problems unsolved.

Problems for the Invention to Solve

Research on a nanometer sized aggregate formed in a solution throughself aggregation of an organic material having a specified structurerevealed the metal oxide nanotubes of the present invention, and thepresent invention offers nanotubes that can be manufactured easily andinexpensively in large quantities, used repeatedly and have the capacityto adsorb and store gases, particularly about 3% by weight of hydrogen.

Means to Solve the Problem

The inventors had already discovered that spiral shaped fibers wereobtained through the self aggregation in water of the compoundrepresented by the chemical formula (Chemical Formula 1) shown below

(in which formula A represents a saccharide radical and R represents analkyl group) (Japanese Patent Application 2001-239014). The inventorsdiscovered that nanotubes consisting solely of a metal oxide could beprepared by utilizing this spiral shaped fiber, and the presentinvention was complete.

That is, spiral shaped fibers are similarly formed when a portion ofCompound (1) is substituted by Compound (2) represented by the chemicalformula (Chemical Formula 2) shown below

(in which formula B represents a saccharide radical and R′ represents ahydrogen atom or an alkyl group). A precursor of a metal oxide isadsorbed on the surface of the spiral shaped surface due to hydrogenbonding of the amino groups [the primary amino groups (—NH₂) and thesecondary amino groups (—NRH)] and the precursor when a precursor (forexample, an alkoxide) of a metal oxide is added. As a result, anaggregate comprising a metal oxide precursor constructed to surround thespiral shaped fiber is formed using the spiral shaped fiber as atemplate.

By adding a catalyst that catalyzes the reaction to form a metal oxide(that is, a structural material binding a metal through an ether typeoxygen) from the metal oxide precursor, a metal oxide structuralmaterial is formed using the spiral shaped fiber as the template. Inthis state, a gel comprising a metal oxide and the aforementionedorganic compound [spiral shaped fibers comprising Compound (1) andCompound (2)] is formed, and nanotubes comprising solely the metal oxideare formed upon removing the organic material by sintering at hightemperatures.

That is, the present invention is a metal oxide nanotube consistingsolely of a metal oxide that may contain hydroxyl groups, which isconstructed in a double spiral and a hollow cylinder and has a holediameter distribution containing two peak hole diameters ranging from 1to 2 nm and from 3 to 7 nm. That is, the nanotube of the presentinvention has two hollow cylinder nanotubes having a hole diameterdistribution with a peak hole diameter of 1-2 nm, particularly 1.2-1.5nm, constructing a double spiral having a peak distance betweennanotubes ranging 3-7 nm, particularly 4-6 nm. The hole diameterdistribution is determined according to Brunauer-Emmett-Teller (BET)method.

The metal oxide nanotube are preferably formed in water or a mixedsolution of water and alcohol by dissolving compound 1 represented bythe chemical formula (chemical formula 1) shown below

and compound 2 represented by the chemical formula (chemical formula 2)shown below

(in the formula A and B, may be identical or different from each other,represent saccharide radicals, R represents an alkyl group and R′represents a hydrogen atom or an alkyl group) in water or a mixedsolution of water and alcohol and allowing to stand.

In the formulae above, A and B may be identical or different from eachother and represent saccharide radicals. In addition, A and B beingidentical saccharide radicals is preferred for efficient formation ofspiral shaped fibers. The saccharide may be monosaccharides,oligosaccharides or polysaccharides, but monosaccharides are preferred.As the monosaccharides, any one of glucose, galactose, N-acetylglucosamine and other hexose, L-arabinose, xylose and other pentose maybe used, but aldopyranose is particularly preferred. Pyranose isavailable in two types, α and β, and either one may be used. As thealdopyranose, glucopyranose, galactopyranose, mannopyranose,allopyranose, altropyranose, gulopyranose, idopyranose, talopyranose andthe like may be used. As the aldopyranose, glucopyranose orgalactopyranose is preferred.

In addition, the term radical refers to a radical from which a hydrogenfrom one of the hydroxyl groups of saccharide has been removed, but aradical obtained by removing a hydrogen from any one of the hydroxylgroups bonded to the six membered aldopyranose ring is preferred.

In addition, the alkanoylamino group (—NHCOR) in Compound (1) may belocated at any one of o-, m- or p-positions in relation to thesaccharide radical (A), but the para position is preferred. The aminogroup (—NR′H) in Compound (2) may be located at any one of o-, m- orp-position in relation to the saccharide radical (B), but the paraposition is preferred.

The R in the Chemical Formula (1) shown above represents an alkyl group.This alkyl group may contain linear or branched chains, but linearchains are preferred. The number of carbon atoms is preferable six totwenty, more preferably ten to twenty, and even more preferably ten tofourteen. As such alkyl groups, the dodecyl group, tridecyl group,tetradecyl group, pentadecyl group, hexadecyl group and the like, forexample, may be used.

In addition, R′ in the Chemical Formula (2) shown above represents ahydrogen atom or an alkyl group, but a hydrogen atom is preferred. Asthe alkyl group, those containing four or fewer carbon atoms arepreferred, and linear chains are more preferred.

Compound (2) can be obtained using an ordinary method of reducing acorresponding nitrophenyl aldopyranoside, and Compound (1) may beobtained by allowing a long chain alkyl fatty acid chloride to reactwith Compound (2).

The metal oxide may be a metal oxide with its precursor adsorbed on theamino groups on the surface of spiral shaped fibers formed fromCompounds (1) and (2). Th metal may be Si, Ti, Zr, Zn, Ba, Ca, Ni, Al,Nb, Ta, W, Hf, Sn, Ge, Mn, Th, Ce or U or mixtures thereof, preferablySi, Ti, Zr, Zn, Ba, Ca, Ni, Al, Nb, Ta, W, Hf or Sn or mixtures thereof,and even more preferably Si, Ti or Zr or mixtures thereof.

Here, a metal oxide does not necessarily need to be represented bycompositional formulae such as ZnO, BaSO₄, CaCO₃, NiO₂, Al₂O₃, NbO₅,WO₃, HfO₂, SnO₂, SiAlO_(3.5), SiTiO₄, ZrTiO₄, AlTiO₅, ZrW₂O₈, SiO₂,GeO₂, TiO₂, MnO₂, ZrO₂, ThO₂, CeO₂ or UO₂, and those containing hydroxylgroups also may be included.

For example, four types of structures surrounding the silicon atom (Q1,Q2, Q3 and Q4) are available in the silicon oxide obtained from alkoxysilica. In one of them, all four bonds are connected to oxygen atomswhich in turn are connected to adjacent silicon atoms (Q4). The secondtype has one of the four bonds terminated with a hydroxyl group andothers connected to oxygen atoms (Q3). The third type has two bondsterminated with hydroxyl groups and the remaining two bonds connected tooxygen atoms (Q2). The last type has three bonds terminated withhydroxyl groups and the remaining bond connected to an oxygen atom (Q1).An examination of the silicon atoms using NMR can distinguish thesestructures and relative proportions. In the case of the silica nanotubesof the present invention, Q4/Q3 values are between 2 and 6.

The inventors discovered that the metal oxide nanotubes are capable ofadsorbing and storing gases, particularly hydrogen, which is consideredto be attributed to having the aforementioned hole diameterdistribution. That is, the present invention is a gasadsorption—desorption and storage material comprising any one of theaforementioned metal oxide nanotubes. More specifically, the presentinvention is a hydrogen adsorption and storage material wherein the gasis hydrogen.

Simile Explanation of the Figures

FIG. 1 shows a field emission scanning electron microscope photograph ofthe double spiral silica nanotubes obtained in Example 1.

FIG. 2 shows a transmission type electron microscope photograph of thedouble spiral silica nanotubes obtained in Example 1.

FIG. 3 shows a transmission type electron microscope photograph (anenergy loss type spectrometer method) of the double spiral silicananotubes obtained in Example 1 before and after sintering. (A) through(C) show the images before sintering, and (D) through (F) show theimages after sintering. (A) and (D) show the images of an entire fiber,(B) and (E) show silicon element distribution diagrams and (C) and (F)show carbon (organic material) element distribution diagrams. Thesemicircles in the lower sections of (D) and (F) represent the vesselsused in the measurements.

FIG. 4 shows a hole diameter distribution curve for the double spiralsilica nanotubes obtained in Example 1.

FIG. 5 shows the structure of the double spiral silica nanotubesobtained in Example 1.

FIG. 6 shows hydrogen adsorption-desorption isothermal curves for thedouble spiral silica nanotubes and cylindrical silica obtained inExample 1. The nanotubes of Example 1 are shown in (A) through (C), and(A), (B) and (C) represent hydrogen adsorption-desorption isothermalcurves at 273K, 288K and 298K, respectively. (D) shows hydrogenadsorption-desorption isothermal curves for the nanotubes of ComparativeExample 1 at 298K.

Embodiment of the Invention

The production process for the metal oxide nanotubes of the presentinvention comprises a step (first step) wherein Compound (1) representedby the chemical formula (Chemical Formula 1) shown below

and Compound (2) represented by the chemical formula (Chemical Formula2) shown below

(in the formulae, A, B, R and R′ are as defined above) are allowed todissolve in water or a mixed solution of water and alcohol and allowedto stand, a step (second step) wherein a metal oxide precursor isfurther mixed, a step (third step) wherein a catalyst designed tofurther convert the metal oxide precursor to a metal oxide is mixed anda step (fourth step) wherein the gel formed in the previous step issintered. The first step through the fourth step is executed in thisorder.

In the first step, Compound (1) and Compound (2) are mixed and dissolvedin water or a water/alcohol mixed solvent. Conducting the first step ina mixed solution of water and alcohol is preferred. The number of carbonatoms in the alcohol is preferably four or less, and methanol, ethanoland propanol are preferred. The proportion of alcohol in the mixedsolution is preferably 10 to 50% by weight. When too much alcohol ispresent in the mixed solution, gel formation does not occur and thecomponents remain dissolved resulting in difficulties in forming extrafine molecular aggregates of spiral shaped fibers effective astemplates. When the alcohol component concentration in the mixedsolution is too low, individual components encounter difficultydispersing and dissolving effectively.

The appropriate concentration of Compound (1) and Compound (2) in thesolvent (a mixed solution) is about 1 to 20 g/liter, but about 5 to 10g/liter is preferred.

A molar ratio of Compound (2) to the sum of Compound (1) and Compound(2) of at least 20% is appropriate, and 20 to 90 mol % is preferred.When this ratio is too low, the molecular aggregate obtained is granularand has difficulty forming fibrous aggregates. Based on the compositionanalyses of the molecular aggregates obtained, about 20% of Compound (2)was found to be present regardless of the ratio at which the componentswere mixed. In order to obtain the desired hollow cylinder shaped microoxide structural material in good efficiency, the presence of 40 to 50%of Compound (2) in an entire solution is most desirable.

Slight heating may be used in the first step to accelerate dissolutionof Compound (1) and Compound (2). The solution is preferably allowed tostand subsequently at room temperature for spiral shaped fibers to formthrough self coagulation of Compound (1) and Compound (2). The timeneeded for the spiral shaped fibers to form can be established uponobserving the gel formation and is ordinarily within half a day.

A metal oxide precursor is blended in the second step after spiralshaped fibers are formed. This metal oxide precursor may be in any formas long as it forms the aforementioned metal oxide, but metal alkoxidesare preferred and alkoxides containing silicon, titanium or zirconiumare more preferred. For example, tetraethoxysilane, tetrapropoxysilane,tetrabutoxysilane, (chloromethyl) triethoxysilane, diethoxymethylsilane,diethoxyisopropylsilane, aminopropyl triethoxysilane, titaniumderivatives of these compounds and zirconium derivatives of thesecompounds may be cited. Tetraethoxysilane, tetraethoxy titanium andtetraethoxy zirconium are preferred based on the ease of raw materialavailability and the cost.

When a metal oxide precursor is added at this step, the metal oxideprecursor is adsorbed on the surface of the molecular aggregates (spiralshaped fibers) formed in the previous step. That is, the anion, a metaloxide precursor, becomes strongly adsorbed on an aggregate surface inthis step through the hydrogen bonding and electrostatic interactionswith Compound (2) partially incorporated into the molecular aggregate(spiral shaped fibers).

The ratio of the metal in a metal oxide precursor to Compound (1) ispreferably 10 to 150 fold equivalent, but 10 to 100 fold equivalent ismore preferred. The mixed reaction solution is allowed to stand forabout a day to 10 days at room temperature. The longer the standingperiod, the greater the adsorption rate of the metal oxide precursor onthe surface of the spiral shaped fiber molecular aggregate and thethicker the hollow cylinder micro metal oxide structure materialobtained after sintering. 4 to 8 days is ideal.

The metal oxide precursor is allowed to polymerize to form a metal oxidein the third step. As described above, this metal oxide may containhydroxyl groups. A basic catalyst is desirable for this polymerization,and ethylamine, propylamine, butylamine, pentylamine, hexylamine,benzylamine, diethylamine, dipropylamine, dibutylamine, dipentylamine,dihexylamine, ammonium hydroxide, alkali metal hydroxides and the likemay be cited. The amount of catalyst used may be in about the sameweight ratio as that of Compound (1) charged. In addition, a pH value ofabout 4 to 10 is appropriate, but 7 to 10 is optimum.

In executing the first step to the third step, the most preferredapproach is to conduct the next step upon completion of the previousstep. However, the next step may be conducted prior to the completion ofthe previous step or before confirming the completion.

In the fourth step, a sintering reaction is conducted to eliminate andremove the organic material from the product of the third step. Usingthis treatment, metal oxide nanotubes comprising solely metal oxide areobtained using molecular aggregates (spiral shaped fibers), an organicmaterial, as templates.

First, the product from the third step is heated for about two hours at100 to 200° C., and the temperature is subsequently raised to 500° C.These procedures are preferably conducted in a nitrogen gas atmosphere.The reason the sintering reaction is initially conducted at relativelylow temperatures is to allow water and alcohol present as the solvent toevaporate slowly at first.

The sintering is subsequently allowed to continue for 4 to 6 hours at500° C. in air. The sintering time is largely dependent on the sampleamount and the sintering device capability. Several hours are neededwhen a small device and milligram sized samples are used, but severaldays of sintering is needed when the samples are in the order of grams.

Effect of the Invention

In the present invention, completely novel nanotubes comprising solelymetal oxide were successfully prepared by utilizing spiral shaped fibersalready discovered (Japanese Patent Application 2001-239014). The metaloxide nanotubes are extremely useful as gas adsorption and storagematerials, particularly to adsorb and store hydrogen. As shown by theexamples, the hydrogen adsorption and storage capacity per unit volumeof the metal oxide nanotubes is extremely high. Therefore, the metaloxide nanotubes are useful in hydrogen manufacturing, storing,transporting and utilization technologies. The utility value is veryhigh, particularly as storage related materials used in hydrogenelectrical generation facilities, as fuel storage materials used inhydrogen fueled vehicles, as fuel cell materials and in other energy andenvironment related areas.

The present invention is illustrated by using the examples below, and itis not intended to restrict the present invention by these. In theexamples shown below, the spiral shaped fibers formed and the nanofiberswere examined using EF-TEM (a transmission type electron microscopeequipped with energy filters) (Nakazawa, I.; Masuda, M.; Okada, Y.;Hanada, T.; Yase, K.; Asai, M.; Shimizu, T. Langmuir 1999, 15, 4757),NMR, FT-IR and XRD. The Rf value obtained by using a hexane/ethylacetate (volume ratio 6/4) mixed solvent as the developing solvent wasdefined as Rfi for thin layer chromatography.

PRODUCTION EXAMPLE 1

p-Nitrophenyl-β-D-glucopyranoside (Tokyo Kasei) (250 mg) was dissolvedin methanol/tetrahydrofuran mixed solvent (20 ml/5 ml), and 10%palladium carbon (250 mg) was added to the solution. Hydrogen gas wasintroduced into the reaction solution for three hours under a nitrogengas atmosphere at room temperature. The reaction mixture was filtered toremove the palladium carbon, and the filtrate was evaporated undervacuum to dry. The solid residue was purified using silica gelchromatography using tetrahydrofuran/chloroform mixed solvent (1/1,volume ratio) as the elution solution to obtainp-aminophenyl-β-D-glucopyranoside.

Yield 80-90%;

-   -   ¹H NMR (300 MHz, DMSO-d₆): δ=3.44-4.10 (m, 6H), 4.76 (s, 2H),        5.25-5.31 (m, 3H), 5.60 (s, 1H), 6.70 (d, J=9.0 Hz, 2H), 6.95        (d, J=9.0 Hz, 2H), 7.37-7.46 (m, 5H); FT-IR (KBr): ν=3312, 2909,        1635, 1510, 1364, 1217, 1089, 1005, 1035, 999, 806, 706 cm⁻¹; MS        (NBA): m/z: 360 [M+H]⁺;

Elemental analysis:

Calculated (%) for C₁₉H₂₁NO₆: C, 63.50; H, 5.89; N, 3.90

Experimental: C, 63.18; H, 6.04; N, 3.78

The p-aminophenyl-β-D-glucopyranoside (250 mg) obtained in the mannerdescribed above was dissolved in tetrahydrofuran (20 ml), and lauroylchloride (300 mg) and triethylamine (1.0 g) were added. The reactionmixture was refluxed for five hours. The reaction solution was filteredto remove the solids, and the filtrate was evaporated under vacuum toprovide solids. The residue was purified using silica gel columnchromatography using methanol/chloroform (1/1, volume ratio) as theelution solution to obtain dodecanoylaminophenyl-β-D-glucopyranoside.

Yield 80%;

-   -   ¹H NMR (300 MHz, CDCl₃): δ=0.9 (t, 3H), 1.5-3.0 (m, 15H),        3.50-4.13 (m, 6H), 4.76 (s, 2H), 5.25-5.31 (m, 3H), 5.63 (s,        1H), 6.70 (d, J=9.0 Hz, 2H), 6.98 (d, J=9.0 Hz, 2H), 7.30 (d,        2H); FT-IR (KBr): ν=3340, 2912, 1630, 1510, 1364, 1217, 1089,        1005, 1035, 999, 806, 706 cm⁻¹; MS (NBA): m/z: 452.27 [M+H]⁺;

Elemental analysis:

Calculated (%) for C₂₄H₃₇NO₇: C, 63.84; H, 8.26; N, 3.10

Experimental: C, 62.15; H, 8.37; N, 3.30

EXAMPLE 1

p-Dodecanoylamino phenyl glucopyranoside (3 mg) obtained in ProductionExample 1 and p-aminophenylglucopyranoside (3 mg) were dissolved inwater-methanol mixed solvent (10:1, volume ratio, 1 ml) by heating thesolution to 70° C. Next, tetraethoxysilane (20 mg) was added, andbenzylamine (6 mg) was subsequently added.

A gel was obtained through gradual cooling and was allowed to standwithout any additional treatment for seven days at room temperaturewithout agitation. The sample was sintered in a nitrogen gas atmospherefirst for two hours at 200° C. and subsequently for four hours at 500°C. to completely remove the organic material. As a result, a metal oxidemicro structure material (metal oxide nanotubes) was obtained.

The metal oxide nanotubes were examined using a transmission typeelectron microscope. A scanning electron microscope photograph is shownin FIG. 1, a transmission electron microscope photograph is shown inFIG. 2. Double spiral shaped fibers comprising two nanotubes wereobserved.

Furthermore, transmission type electron microscope photographs (energyloss type spectrometric method) of the double spiral silica nanotubesobtained before and after sintering are shown in FIG. 3. By conductingan electron microscope examination employing an energy loss typespectrometric method (for example, Japan Petrochemical Society Journal,Vol. 47, No. 10, pp. 197-203, 1998), element distribution diagrams ofthe nano structure for silicon and carbon were prepared. The presence ofsilicon (B) and carbon (that is, organic materials) (C) was confirmedprior to sintering (A-C), but the presence of only silicon (E) wasconfirmed (D-F) and no carbon (F) was detected after sintering. Theresults indicated that the organic material was completely removed fromthe template.

Using the metal oxide nanotubes obtained, an adsorption—desorptionisothermic curve for nitrogen gas was obtained using aBrunauer-Emmett-Teller (BET) method. That is, metal oxide nanotubes werecompletely degassed under high vacuum at 300° C. for 71 hours and wereslowly cooled to room temperature. Next, a known amount of nitrogen gaswas continuously added to the sample cell under liquid nitrogentemperature conditions (about −195° C.), and the pressure was measured.By repeating this procedure, adsorption isotherms were obtained.Similarly, desorption isotherms were obtained by measuring the amount ofgas released from a sample when relative pressures were graduallylowered from one. The hole diameter size-volume curve shown in FIG. 4was obtained.

As a result, two peak hole diameters (the peaks in the curve shown inFIG. 4) were observed, and the hole area in the metal oxide nanotubeswas found to be 450-500 m/g. Of these two peak hole diameters (1.2-1.5nm and about 5 nm), the hole diameter of 1.2-1.5 nm was attributed tothe hollow cylinder present in the center of individual double spiralnanotubes and the hole diameter of about 5 nm was attributed to the nanospace formed between two nanotubes.

Based on these results, the nanotubes were thought to be composed solelyof a metal oxide and were thought to constitute double spiral (thedistance between two nanotubes was about 5 nm) hollow cylinder shapednanotubes having external diameters of about 2.5 nm, internal diametersof about 1.2-1.5 nm and lengths of several hundred micrometers as shownin FIG. 5.

In addition, the gas adsorption—desorption rate was calculated using theweight change rate observed when the metal oxide nanotubes obtained werecompletely degassed using the same method used to adsorb and desorbnitrogen gas, hydrogen gas was introduced at constant temperature bychanging the pressure from 1 MPa to 10 MPa, and adsorption—desorptionisothermic curves were obtained. The hydrogen adsorption—desorptionisothermic curve of the double spiral silica nanotubes obtained inExample 1 is shown in FIG. 6.

The hydrogen adsorption capacity of the metal oxide nanotubes at 10 MPaand 273 K was 3.66% by weight (curve A). Similarly, the hydrogenadsorption capacity of the metal oxide nanotubes at 10 MPa and 288 K wasabout 3.22% by weight (curve B) and at 10 MPa and 298 K was about 3.0%by weight (curve C).

EXAMPLE 2

p-Dodecanoylamino phenylgalactopyranoside was used in place ofp-dodecanoylamino phenylglucopyranoside in Example 1 and p-aminophenylgalactopyranoside was used in place of p-aminophenyl glucopyranoside toconduct the same operations described in Example 1, and similar doublespiral silica nanotubes were obtained.

EXAMPLE 3

p-Tetradecanoylamino phenylglucopyranoside was used in place ofp-dodecanoylamino phenylglucopyranoside in Example 1 to conduct the sameoperations described in Example 1, and, similarly, double spiral silicananotubes were obtained.

EXAMPLE 4

Hexylamine was used in place of benzylamine in Example 1 to conduct thesame operations described in Example 1, and, similarly, double spiralsilica nanotubes were obtained.

COMPARATIVE EXAMPLE 1

A potassium complex was obtained by dissolving a gel forming agent (5mg) containing cholesterol and diazacrown ether segments at both ends ofthe molecules in one gram of dichloromethane in the presence of anequimolar amount of potassium perchlorate. The potassium complex wasadded to 1-butanol (95 mg) containing tetraethoxy silane (15 mg) andbenzylamine (6 mg), and the mixture was heated to facilitatedissolution. The solution was left standing for a day at roomtemperature. The gel obtained was dried in vacuum, and multilayeredsilica nanotubes having an internal diameter of about 300 nm to 500 nmwere obtained by subsequently drying and sintering the gel for an hourat 200° C. and two hours at 500° C. under nitrogen gas atmosphere andfurther for four hours at 500° C. in air [J. H. Jung, Y. Ono, S.Shinkai, Langmuir, 16, 1643 (2000)].

The hydrogen adsorption and storage capacity of the multilayered silicananotubes was evaluated and was found to be 0.58% by weight at 10 MPaand 298K. (FIG. 6, Curve D.)

1. A metal oxide nanotube consisting solely of a metal oxide that maycontain hydroxyl groups, which is constructed in a double spiral and ahollow cylinder and has a hole diameter distribution containing two peakhole diameters ranging from 1 to 2 nm and from 3 to 7 nm.
 2. The metaloxide nanotube as in claim 1 wherein the metal is Si, Ti or Zr ormixtures thereof.
 3. The metal oxide nanotube as in claim 1 being formedusing spiral shaped fibers as a template, which are formed by dissolvingcompound 1 represented by chemical formula 1

and compound 2 represented by chemical formula 2

in water or a mixed solution of water and alcohol, wherein A and Brepresent saccharide radicals that may be identical or different fromeach other, R represents an alkyl group and R′ represents a hydrogenatom or an alkyl group, and allowing the resulting solution to stand. 4.A gas adsorption and storage material comprising the metal oxidenanotube as in claim
 1. 5. A hydrogen adsorption and storage materialcomprising the metal oxide nanotube as in claim
 1. 6. A method formanufacturing a metal oxide nanotube comprising the steps of dissolvingcompound 1 represented by chemical formula 1

and compound 2 represented by chemical formula 2

in water or a mixed solution of water and alcohol, wherein A and Brepresent saccharide radicals that may be identical or different fromeach other, R represents an alkyl group and R′ represents a hydrogenatom or an alkyl group, allowing the resulting solution to stand, mixingfurther a metal oxide precursor and a catalyst for converting the metaloxide precursor into a metal oxide into the solution whereby a gel isformed, and sintering the gel.
 7. The method as in claim 6 wherein themetal is Si, Ti or Zr or a mixture thereof.
 8. The method as in claim 6wherein the metal oxide precursor is an alkoxide of said metal.
 9. Themethod as in claim 6 wherein compound 1 and compound 2 are dissolved ina mixed solution of water and an alcohol having four carbon atoms orless, and the content of alcohol in the mixed solution is 10 to 50% byweight.
 10. The method as in claim 6 wherein the catalyst is a basiccatalyst.
 11. The method as in claim 6 wherein the ratio of compound 1to the sum total of compounds 1 and 2 is 20 to 90 mol % and the ratio ofmetal in the metal oxide precursor to compound 1 is 10 to 150 foldequivalent.
 12. The method as in claim 6 wherein A and B may beidentical or different from each other and represent radicals obtainedby removing hydrogen from any one of the hydroxyl groups bonded to analdopyranose six membered ring.
 13. The method as in claim 12 whereinthe aldopyranose is glucopyranose or galactopyranose.
 14. The method asin claim 6 wherein the alkanoylamino group (—NHCOR) of compound 1 islocated in a para position to the saccharide radical A, the amino group(—NR′H) of compound 2 is located in a para position to the saccharideradical B, A and B are identical saccharide radicals, R is a linearalkyl group having six to twenty carbon atoms and R′ is a hydrogen atom.15. A metal oxide nanotube as in claim 2 being formed using spiralshaped fibers as a template, which are formed by dissolving compound 1represented by the chemical formula 1

and compound 2 represented by chemical formula 2

in water or a mixed solution of water and alcohol, wherein A and Brepresent saccharide radicals that may be identical or different fromeach other, R represents an alkyl group and R′ represents a hydrogenatom or an alkyl group, and allowing the resulting solution to stand.16. A gas adsorption and storage material comprising the metal oxidenanotube as in claim
 2. 17. A gas adsorption and storage materialcomprising the metal oxide nanotube as in claim
 3. 18. A gas adsorptionand storage material comprising the metal oxide nanotube as in claim 15.19. A hydrogen adsorption and storage material comprising the metaloxide nanotubes as in claim
 2. 20. A hydrogen adsorption and storagematerial comprising the metal oxide nanotubes as in claim
 3. 21. Ahydrogen adsorption and storage material comprising the metal oxidenanotubes as in claim
 15. 22. The method as in claim 7 wherein the metaloxide precursor is an alkoxide of said metal.
 23. The method as in claim22 wherein compound 1 and compound 2 are dissolved in a mixed solutionof water and alcohol having four carbon atoms or less and the content ofalcohol in the mixed solution is 10 to 50% by weight.
 24. The method asin claim 23 wherein the catalyst is a basic catalyst.
 25. The method asin claim 24 wherein the ratio of compound 1 to the sum total of thecompounds 1 and 2 is 20 to 90 mol % and the ratio of metal in the metaloxide precursor to the compound 1 is 10 to 150 fold equivalent.
 26. Themethod as in claim 25 wherein A and B may be identical or different fromeach other and represent radicals obtained by removing hydrogen from anyone of the hydroxyl groups bonded to an aldopyranose six membered ring.27. The method as in claim 26 wherein the aldopyranose is glucopyranoseor galactopyranose.
 28. The method as in claim 27 wherein thealkanoylamino group (—NHCOR) of compound 1 is located in a para positionto the saccharide radical A, the amino group (—NR′H) of compound 2 islocated in a para position to the saccharide B radical, A and B areidentical saccharide radicals, R is a linear alkyl group having six totwenty carbon atoms and R′ is a hydrogen atom.